As shown in FIG. 11(A) schematically, a bead portion (a) of a pneumatic tire is provided with an annular bead core (c) made of a hard steel wire and the like to fix both ends of the carcass (b) securely and to prevent from dropping-off of a rim. The radially outer circumferential surface of the bead core (c) is provided with bead apex rubber (d) having a triangle shape in cross-section to improve bead durability and steering stability and the like. This bead apex rubber (d) is gone into a tire manufacturing line as a bead apex rubber-core joint body jointed integrally with the bead core (c) in advance (hereinafter called a “core joint body”).
As the forming method of the core joint body, heretofore, as shown in FIG. 11(B), the bead apex rubber (d) having the triangle shape in cross-section extruded and formed with a rubber extruder is wrapped once on the outer circumferential surface of the bead core (c). Then both wrapping ends of tip portion and back-end portion are butted and jointed. At this time, the bead apex rubber (d) having a high temperature just after molding is soft and deformable. Therefore, to feed the bead apex rubber (d) just after molding to the bead core is not easy. It needs to once cool down after molding.
However, the cooling deteriorates adherence property of the bead apex rubber (d). In consequence, the lack of adhesion makes it easier to fall away the bead apex rubber (d) from the bead core (c) (see FIG. 12(A)). The cross-sectional shape deforms such as shrinking and curling of the bead apex rubber (d) in the width direction (see FIG. 12(B)). In the event of the severe curl, a tip portion (d1) and a back-end portion (d2) cannot be jointed. when the cross-sectional height of the bead apex rubber (d) is large, the bead apex rubber (d) falls due to the curl and it makes difficult to form the core joint body. Also there is problems that the joint portion drops off between the tip portion (d1) and the back-end portion (d2) owing to adhesion insufficiency (see FIG. 12(C)), and a gap (f) between the tip portion (d1) and the back-end portion (d2) (see FIG. 12(D)) and overlapping (g) between the tip portion (d1) and the back-end portion (d2) (see FIG. 12(E)) causes weight unbalance.
As a conventional device of the bead apex rubber to the bead core is known as the following Patent Documents 1 and 2.